Precision speed control



P 1950 f A. F. FAIRBANKS 2,523,503

PRECISION SPEED comm.

Filed April 26, 1949 2 Sheets-Sheet 1 2 sync. POWER AMPLIFIER .3.

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INVENTOR.

AVAR D F. FAIRBANKS ATTORNEY S p 1950 A. F. FAIRBANKS 2,523,503

PRECISION SPEED com'xor.

Filed April 26, 1949 2 Sheets-Sheet 2 INVENTOR. AVARP F. HIRBANKSATTORNEY Patented Sept. 26, 1950 OFFICE PRECISION SPEED CONTROL Avard F.Fairbanks, Los Angeles, Calif., assign(- to North American Aviation,Inc.

Application April 26, 1949, Serial No. 89,688

6 Claims. (Cl. 3188) This invention pertains to adjustment of speed of ashaft rotation. It particularly pertains to obtaining a shaft rotationof highly constant speed which speed is capable of precision adjustmentover pre-determined limits.

It is an object of this invention to provide means for rotating a shaftat a highly constant speed while providing for precise adjustment of thespeed.

It is another object of this invention to provide means for adjustingthe speed of a shaft driven by a synchronous motor.

It is a further object of this invention to provide a crystal controlledsynchronous motor with remote adjustable speed.

It is still a further object of this invention to provide a crystalcontrolled synchronous motor with a speed remotely adjustable by radioor other communication device.

Other objects of invention will become apparent from the followingdescription taken in connection with the accompanying drawings in which:

Fig. 1 is a block diagram of the invention;

Fig. 2 is a detailed schematic of the decimal place selector of theinvention; and

Fig. 3 is a detailed schematic of a typical digit selector, pulse gate,and step motor of the invention.

Referring to Fig. 1, a crystal oscillator l emits constant frequencypulses of frequency f1 to power amplifier 2 which drives synchronousmotor 3 at constant speed. A second frequency f2, generated byoscillator l is fed via frequency divider 4 to step charge divider 5 andpulse amplifier 6 whose output is a repeated series of 10 stepped pulsesas shown at 1 in Fig. 1. This series of pulses is fed in parallel topulse gates 8, 9, l0 and H which drive step motors l2, l3, l4 and I5which are mechanically connected to differentials I6, ll, 18 and i9.Differential I6 has a gear ratio of 1:1 while differentials ll, l8, andI9 have gear ratios of 1:10, 1:100, and l:1000 respectively. Synchronousmotor 3 is shaft connected to difierentials l6, I7, l8 and I9 and load25 so that load 25 is driven at the synchronous speed of motor 3 plusthe speed of step motors I2, [3, l4 and I5 as reduced by the gear ratiosof diiferentials [6, I1, i8 and I9. Pulse gates 8, 9, l0 and ll arecontrolled by digit selectors 20, 2|, 22 and 23 which in turn arecontrolled by decimal place selector 24 which receives control signalsby radio.

Referring now to Fig. 2, there is shown a detailed schematic of decimalplace selector 24.

Vacuum tubes 26 and 21 which may also be thyratrons, receive radiotransmitted pulses and in turn control rotary switches 28 and 29 whichare connected to operate together. Switch 29 is turned by step motor 30which takes a step in angular movement every time inductance 3| receivesa pulse from tube 21.

Digit selectors 20, 2|, 22 and 23 are illustrated typically in Fig. 3where step motor 32 is driven by pulses from tube 26 through switch 29in Fig. 2 by means of inductance 33. Motion of step motor 32 causesswitch 34 to move to successive positions on tapped resistance 35 withten taps. Such movement causes change in the grid bias of tube 36,resistance 35 being connected to a source of negative voltage such asvolts as an example. Pulses from pulse amplifier 6 are fed to the gridof tube 36 via condenser 31 and the pulse output of tube 36 drives stepmotor l2 which in turn supplies a mechanical rotation to differential 5.

As an example of the operation of the invention let it be required thatload 25 be driven with a speed of 10.5432 revolutions per second withspeed remotely adjustable between 10.0000 revolutions per second and11.0000 revolutions per second. The frequency fl is then chosen so thatsynchronous motor 3 is driven at 10 revolutions per second. Since motor3 is connected to load 25 by differentials l6, ll, 18 and 19, load 25 isdriven at 10 R. P. S. plus whatever rotations are supplied by saiddifferentials. Differential I6, having a gear ratio of 1:1 is capable ofsupplying rotations of 0 to l revolution per second in multiples of .1revolution per second. Similarly differentials l1, l8, and I9 supplyhundr-edths, thousandths, and ten-thousandths of a revolution persecond.

To set into the device the precise angular velocity desired, continuingas an example the requirements for a load speed of 10.5432 revolutionsper second, a decimal selection pulse is supplied to the grid of tube2'! which brings switch 29 to position 20. Then five digit selectorpulses are supplied to tube 26 which in turn are supplied to step motor32 which takes five steps leaving switch 34 on the fifth tap ofresistance 35, thus supplying a predetermined grid bias to tube 36.

At this point it must be recalled that condenser 31 is supplying pulsesfrom pulse amplifier 6 which are stepped in form. For the purpose ofillustration, they might be furnished as a series of ten stepped pulsesgraduated from 0 to 100 volts in steps of 10 volts and furnished at therate of 10 steps or one complete series of pulses every secnd. But thebias on tube 36 is adjusted, as hereinbefore described, so that only ofeach series of pulses are allowed to affect the flow of electrons intube 36. The effect of varying the grid bias of tube 36 therefore is toclip" of! a predetermined number of the pulses in each group of tencoming from pulse amplifier 6. Therefore, to continue the above example,only five pulses are emitted by tube 36 per second so step motor i2 isstepped forward five times per second. Assuming that step motor 12 isdevised to rotate one full revolution per ten steps, the angularvelocity contributed to driving load 25 by the motion of step motor I2is .5 R. P. S. The rotation of synchronous motor 3 together with therotation of step motor l2 supply a rotation of 10.5 R. P. S. todifferential H.

In a similar manner, decimal selector 2| is then moved successively toswitch positions 2 i, 22 and 23 and the biases on pulse gates 3, i0 andII are set so as to allow 4, 3 and 2 pulses respectively of each groupof ten from pulse amplifier 6 to pass to step motors l3, l4 and I5respectively. Then, differentials l1, l8 and i9, having reduced gearratios, supply the 100ths, 1000ths, and 10,000ths of a R. P. S.rotations to load 25 making the final velocity of load 25 the required10.5432 R. P. S.

After the apparatus is thus set up for the required rotational velocity,step motor 30 is pulsed again disengaging switch 23 from switch position23 and bringing switch 23 to position P which then supplies platecurrent to the pulse gates. The device is then ready for operation atthe adjusted speed. If it is desired to change the speed setting, anadditional pulse is fed to step motor 30 which brings switch 28 toposition R to thus energize a reset device (not shown) which returns allswitches to initial position after which a new speed may be set into thedevice in the manner previously stated.

By use of different gear ratios in differentials i6, ll, i8 and I9 andby use of a greater or smaller number of digit selectors, pulse gates,and differentials a speed with any predetermined range of precisionadjustment may be obtained by this invention. Furthermore, since thesynchronous motor is driven by the amplified output of a crystalcontrolled oscillator whose frequency has been divided many times, theangular velocity obtained is highly exact.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by terms of the appendedclaims.

I claim:

1. Means for rotating a load at an adjustable constant speed comprisingmeans for producing a constant speed shaft rotation, a plurality ofmechanical differentials arranged in series between said constant speedmeans and said load, means for producing groups of energy pulses at apredetermined rate, adjustable means for selecting a predeterminednumber of pulses from each of said groups, and means for driving saiddifferentials at a speed which is a function of the number of saidselected pulses thereby to rotate said load at an adjustable constantspeed.

2. A device as recited in claim 1 in which said means for drivingcomprise step motors capable of a fraction of a revolution per selectedpulse, in which said means for producin groups of energy pulsescomprises a step charge divider, and in which said means for selectingpulses is a biased electronic valve which transmits all pulses havingamplitude above the value of the bias.

3. Means for rotating a load at an adjustable constant speed comprisingmeans for producing energy pulses at constant frequency, means forproducing grouped energy pulses at constant frequency, adjustable meansfor selecting predetermined numbers of pulses from each of said groupsof pulses and means for producing a rotation proportional to the sum ofsaid constant frequency pulses and said selected pulses per unit time.

4. Means for rotating a load at an adlustable constant speed comprisingmeans for producing energy pulses at constant frequency, means forproducing grouped energy pulses at constant frequency, adjustable meansfor selecting predetermined numbers of pulses from each of said groupsof pulses, a synchronous motor adapted to be driven by said constantfrequency pulses, a plurality of differentials connecting said motor tosaid load in series and means for driving said diflerentials at speedsproportional to the frequency of said selected pulses to thereby drivesaid load at the speed of said synchronous motor plus a speed which is apredetermined function of the speeds of said differential driving means.

5. Means for producing an adjustable constant speed shaft rotationcomprising a synchronous motor, crystal controlled means for drivingsaid synchronous motor at constant speed, means for producing arepetitive series of pulses of electrical energy at a frequency of whichthe frequency of said crystal controlled means is a common denominatorand at an amplitude which varies in steps which are multiples of apredetermined amplitude, a plurality of differentials drivinglyconnected in series between said synchronous motor and the shaft whosespeed must be constant but adjustable, a plurality of step motors fordriving said differentials, electronic valve means for transmitting saidstepped pulses to said step motors, and remotely controllable means foradjusting the bias on said electronic valve means to allow to pass apredetermined number of said stepped pulses in each repetitive series,whereby the shaft speed attained is caused to depend on the sum of thespeeds of said synchronous motor and said step motors.

6. Means for rotating a load at a remotely adjustable constant speedcomprising means for producing a constant speed shaft rotation, aplurality of mechanical differentials arranged in series between saidconstant speed means and said load, means for producing groups ofelectrical pulses at a predetermined rate, remotely controllableadjustable means for selecting a predetermined number of .pulses fromeach of said groups, and means for driving said differentials at a speedproportional to the number of said selected pulses to thereby rotatesaid load at a con stant remotely adjustable speed.

AVARD F. FAIRBANKS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,300,424 Jones Nov. 3, 1942 2,34,877 Troflrnov Apr. 18, 1944 2,433,194 Bedford et al. Dec. 23, 1947

